Climate change constitutes one of the greatest environmental challenges. The increase in carbon dioxide concentration in the atmosphere is in very large part the cause of global warming. CO2 of human origin is essentially emitted into the atmosphere through the combustion of fossil fuels in thermal power stations.
Thermal power stations, by burning fuels, release heat that can be used to produce steam and optionally mechanical or electrical energy. The flue gases release large quantities of CO2 into the atmosphere.
To combat CO2 emissions, one technology aims to capture the CO2 emitted during the combustion of carbon-containing fuels in order to transport and/or sequester it underground. However, in order for such CO2 capture to be possible, some of the flue gases have to be compressed up to a pressure of typically around 4 to 60 bar abs before being purified and then further compressed up to a pressure of typically 100 to 200 bar abs in order to be sequestered.
The technology for compressing gases in so high a volume and to such compression levels requires at the present time the use of centrifugal compressors in which bladed wheels eject gas centrifugally. To reduce the energy consumption, these compressors are multi-staged, a refrigerant being used to bring the gas down to ambient temperature at each stage.
Both compression wheels and interstage heat exchangers are subject to being fouled by the solid particles resulting from the combustion. The particles may block heat exchangers and reduce their thermal capabilities. As regards compressor wheels, these may become unbalanced by the nonuniform build-up of mass on the wheels. This results in mechanical shaft imbalance, vibrations and potentially machine destruction.
Another technology for compressing gases in so large a volume is what is called “axial” technology, in which rotor fins, rotating at high speed, alternating with stationary stator fins, compress the gas along the axis of the rotor of the machine. In such a technology, the presence of solid particles results in a loss of material on the fins, especially by erosion.
The situation is therefore confronted with a dust collection problem. The term “dust collection” is understood to mean any action or process in which a smoke or a gas is stripped of a substantial fraction of the solids that it contains by a gas/solid separation. Items of apparatus or equipment performing this task are called dust collectors or dust separators.
As mentioned in the document by B. Siret, entitled “Dépoussiérage et dévésiculage [Dust and mist collection]”, Techniques de l'Ingénieur, J 3 580, pages 1 to 26, the technologies traditionally installed for solving the dust collection problem when a carbon-containing fuel is burnt are of various types, among which the following may be distinguished:                electrostatic filters in which the charged particles are removed from the flue gas stream;        bag filters in which the flue gases pass through a filter cloth;        cyclones in which the particles are separated by centrifugation and acceleration; and        scrubbers in which the flue gases are brought into contact with a liquid shower.        
These technologies serve to lower the dust content from conventional levels of grams or tens of grams per cubic meter at the boiler outlet to levels a thousand times lower, in line with the usual standards for discharging into the atmosphere, but always greater than 1 mg/m3.
However, with a flue gas dust content of 1 mg/m3 or higher, the compression operation will suffer clogging, especially in the intermediate refrigerants, requiring stoppages for frequent maintenance. Moreover, this degrades the compression performance.
Starting from this situation, a problem that arises is how to provide a process for the combustion of carbon-containing fuels with improved flue gas treatment, especially a treatment suitable for centrifugal compressor technology.